Macrophage factor controlling differentiation of B cells.

Peritoneal macrophages of the mouse produce, in response to cell wall components of Gram-negative bacteria (lipopolysaccharide and lipoproteins), a factor that causes antigen-stimulated B cells of differentiate into antibody-producing cells. Unlike lipopolysaccharide, this factor is not mitogenic for B cells. Production of the macrophage factor does not depend on participation of T cells or other accessory cells since it is readily produced by several cloned macrophage cell lines as well as by peritoneal macrophages of athymic nude mice. The factor is active only in conjunction with antigen. T cells, although apparently not necessary, amplify its effect. The factor induces phenotypic differentiation of B cell precursors as selectively as thymopoietin induces differentiation of prothymocytes.